The purpose of this study is to examine the possibility that bronchial asthma might be associated with a disturbance in the metabolism in cyclic AMP. At the present time, the evidence in such a disturbance in cellular function is largely indirect and the mechanisms which might be responsible have not been established. Our approach to the problem is based on direct measurement of cyclic AMP in leukocytes obtained from the peripheral blood of normal and asthmatic subjects. Comparisons are made of the results in unstimulated cells and in leukocytes which have been exposed to pharmacologic agents either in vivo or in vitro. The responses of asthematic subjects are evaluated in relation to the presence or absence of symptoms and in relation to the results of normal subjects.